What type of polarization is supported by ground-wave propagation?

Ground-wave propagation relies on radio waves traveling close to the Earth's surface. For a wave to propagate effectively along the ground, it must be vertically polarized. If horizontal polarization is used, the electric field is parallel to the ground. The Earth acts somewhat like a short circuit to horizontal electric fields, causing the wave's energy to be absorbed and dissipated very rapidly. Vertical polarization minimizes this short-circuiting effect, allowing the wave to travel much further. This principle explains why AM broadcast stations, which rely heavily on ground-wave propagation to cover local areas during the day, utilize tall vertical antennas.